The present invention relates to a liquid composition polymerizable into organic glass.
More specifically, the present invention relates to a liquid composition which can be polymerized, by means of radicalic polymerization, into organic glass with a refractive index (nD20)xe2x89xa71.53, having good optical and physico-mechanical properties, and good dyeability, comprising the product obtained from the transesterification of a mixture of diallyl carbonate (A) and a phthalic ester (B), with one or more polyols (C), linear or branched, containing from two to eight carbon atoms in the molecule, a process for its preparation and its use in the preparation of organic glass.
A further object of the present invention relates to the organic glass obtained from the polymerization of said composition and the end-products obtained starting from said composition such as, for example, ophthalmic lenses and lenses for optical instruments.
Organic glass obtained from the polymerization of bis(allyl carbonate of diethylene glycol has been known and used for many years in this specific field. The use of the above organic glass, however, in the preparation of optical articles such as, for example, ophthalmic lenses, has various disadvantages mainly due to their relatively low refractive index (nD20) in the order of 1.50.
As a result of this, especially in the case of high power ophthalmic lenses, these lenses have poorer aesthetic characteristics owing to the greater thickness and also lose the advantages of lightness due to the limited specific weight.
In order to overcome these drawbacks, compositions polymerizable into organic glass having a higher refractive index, have been prepared in the known art.
To achieve this objective, resort has been made to the introduction, in the above compositions, of reactive monomers or comonomers containing aromatic groups: among these, those consisting of allyl esters of aromatic carboxylic acids such as, for example, diallyl orthophthalate, diallyl isophthalate, diallyl terephthalate, triallyl trimellitate, etc., are of particular interest.
The introduction of the above species allows the refractive index (nD20) to be increased up to values ranging from 1.53 to 1.57 and gives the optical articles produced good mechanical properties and thermal resistance.
Polymerizable compositions of the above type are described, for example, in European patent applications: EP 371,140, EP 392,514, EP 472,161 and EP 305,048.
Optionally, the diallylphthalate is added to the above compositions in the form of xe2x80x9cdiallylphthalate componentxe2x80x9d which consists of the product obtained from the reaction between diallyl phthalate and a glycol as described, for example, in the following European patent applications: EP 540,003 and EP 540,043.
In the above European patent applications, bis(allyl carbonate) of diethylene glycol is indicated as second component of the polymerizable compositions. These compositions are polymerized into organic glass having a refractive index (nD20) equal to or higher than 1.53 using organic peroxides as polymerization initiators. The optic glass thus obtained has higher transparency characteristics, mechanical resistance to solvents, etc.
It has various disadvantages, however, linked to the fact that the components of the above polymerizable compositions have different reactivity and chemical characteristics. This makes it more difficult to control the polymerization reaction and results in the production of a polymeric end-product (for example, lenses) having a composition and properties which are not homogeneously distributed in the mass. This is demonstrated by the fact that the lenses obtained from the polymerization of said compositions, when observed in polarized light, have tensioned zones which can jeopardize their dimensional stability or create problems in the assembly phase of glasses.
The main problems, however, arise in the coloring operations of the above lenses, by immerging them in color baths using the known xe2x80x9cdip dyeingxe2x80x9d technique. In fact, the colored lenses thus obtained do not have uniform coloring due to the presence of areas with differing intensities. As color uniformity is one of the basic parameters which an optical article, such as an ophthalmic lens, must guarantee, the above problem is particularly serious.
The Applicant has now found that it is possible to overcome the above drawbacks of the known art by using a polymerizable liquid composition comprising mixed oligomers of allyl esters of aromatic carboxylic acids and aliphatic allyl carbonates, polymerized in the presence of organic polymerization initiators.
In particular, the Applicant has surprisingly found that the polymerizable liquid compositions object of the present invention, can be advantageously used for the preparation of organic glass having a refractive index (nD20)xe2x89xa71.53, an excellent combination of optical and physico-mechanical properties and good dyeability by immersion in color baths.
An object of the present invention therefore relates to a liquid composition polymerizable, by means of radicalic polymerization, into organic glass, comprising the product obtained from the transesterification of a mixture of diallyl carbonate (A) and a phthalic ester (B), with one or more polyols (C), linear or branched, containing from two to eight carbon atoms in the molecule.
In the liquid composition object of the present invention, the molar ratio (A+B)/C ranges from 2/1 to 7/1 and the molar concentration of (B) in the mixture (A+B) ranges from 10% to 70% with respect to the total of said mixture (A+B).
In the polymerizable liquid composition object of the present invention, the molar ratio (A+B)/C preferably ranges from 2.5/1 to 5/1 and the molar concentration of (B) in the mixture (A+B) ranges from 20% to 60% with respect to the total of said mixture (A+B).
Phthalic esters (B) which can be used for the purposes of the present invention, are ortho, meta or paraphthalates of aliphatic alcohols containing from 1 to 3 carbon atoms in the molecule.
Specific examples of phthalic esters (B) useful for the purposes of the present invention are: dimethyl orthophthalate, dimethyl isophthalate, dimethyl terephthalate, diethyl orthophthalate, diethyl isophthalate, diethyl terephthalate, dipropyl orthophthalate, dipropyl isophthalate, dipropyl terephthalate, diallyl orthophthalate, diallyl isophthalate, diallyl terephthalate, etc.
Preferred phthalic esters for the purposes of the present invention are: dimethyl isophthalate, dimethyl terephthalate, diallyl isophthalate and diallyl terephthalate.
When a phthalic ester different from diallyl orthophthalate, diallyl isophthalate or diallyl terephthalate is used as component (B), allyl alcohol (D) must be added to the reaction mixture in a molar quantity equal to about 1-3 times that of the phthalate (B) to ensure that the reaction product exclusively consists of species having chain-end allyl functionalities.
Polyols (C) which can be used for the purposes of the present invention are polyols consisting of linear or branched aliphatic glycols, containing from two to eight carbon atoms in the molecule.
Specific examples of glycols useful for the purposes of the present invention are: ethylene glycol, diethylene glycol, triethylene glycol, tetra-ethylene glycol, 1,4-butanediol, 1,6-hexanediol, 1,3-propanediol, neopentylglycol, dipropyleneglycol, 2,2,4-trimethyl-1,3-pentanediol, etc.
Diethylene glycol is the preferred glycol for the purposes of the present invention.
Polyols (C) which can be used for the purposes of the present invention are also linear or branched aliphatic polyols containing from four to twenty carbon atoms and from three to six hydroxyl groups in the molecule.
Specific examples of polyols (C) containing from four to twenty carbon atoms and from three to six hydroxyl groups in the molecule useful for the purposes of the present invention are: pentaerythritol, trimethylolpropane, dipentaerythritol, ditrimethylolpropane, tris(hydroxyethyl)isocyanurate, etc.
Preferred polyols (C) containing from four to twenty carbon atoms and from three to six hydroxyl groups in the molecule for the purposes of the present invention are: pentaerythritol and trimethylolpropane.
For the purposes of the present invention, said polyols (C) containing from four to twenty carbon atoms and from three to six hydroxyl groups in the molecule, can only be used in the reaction mixture as a combination with the glycols described above in a concentration not exceeding 20% by weight with respect to the total weight of the mixture of polyols (C). Concentrations higher than 20%, in fact, cause an excessive increase in the viscosity of the polymerizable liquid composition and a deterioration in some of the properties of the end-products obtained from their processing, mainly their impact strength.
The polymerizable liquid composition object of the present invention is obtained starting from the mixture of diallyl carbonate (A), phthalic ester (B), polyol (C), and optionally, allyl alcohol (D), operating under transesterification conditions. More specifically, the reagents are put in contact with each other, in the proportions indicated above, and reacted at a temperature ranging from 80xc2x0 C. to 160xc2x0 C., preferably from 90xc2x0 C. to 130xc2x0 C., in the presence of a catalyst of the alkaline type, the low-boiling products which are formed as reaction by-product, being continually eliminated.
Catalysts of the alkaline type which can be used for the purposes of the present invention are: hydroxides, carbonates and alcoholates of alkaline metals, organic bases, basic ionic exchange resins.
Specific examples of catalysts of the alkaline type useful for the purposes of the present invention are: sodium hydroxide, sodium carbonate, sodium methylate.
The catalyst is conveniently used in a quantity equal to at least 1 ppm (parts per million by weight) with respect to the weight of the component (C) and, preferably, in a quantity ranging from 0.01% to 0.3% by weight.
The above transesterification reaction is conveniently carried out at such a pressure as to make the system boil at the pre-selected operating temperature, in order to favour the elimination of the low-boiling products from the reaction mixture: for example, pressure values ranging from 50 mbars and 1030 mbars, preferably from 60 mbars to 800 mbars, are suitable for the purpose.
The reaction is considered as being complete when all the theoretical allyl alcohol deriving from the reaction itself and, optionally, the excess allyl alcohol which may be present when a phthalic ester different from diallyl orthophthalate, diallyl isophthalate or diallyl terephthalate is used as component (B), have been extracted.
Operating under the conditions described above, the reaction times generally range from 0.5 hours to 20 hours, preferably from 1 hour to 10 hours.
After cooling to about 70xc2x0 C., the above reaction mixture is washed with water to remove the small quantities of residual catalyst and, after the de-mixing and separation of the aqueous phase, the non-reacted diallyl carbonate is eliminated, by heating to a temperature in the order of 130xc2x0 C., under a decreasing pressure with end-values ranging from 0.1 mbars to 20 mbars, preferably from 0.5 mbars to 2 mbars, obtaining the desired composition as residue.
The composition thus obtained is finally subjected to filtration after optional treatment with activated carbon.
The composition object of the present invention is liquid at room temperature and has viscosity values ranging from 15 cst to 300 cst and density values ranging from 1.1 g/ml to 1.3 g/ml.
The polymerizable liquid composition object of the present invention is a complex mixture which contains diallyl phthalate, bis(allyl carbonate) of component (C) in monomeric and oligomeric form, bis(allyl phthalate) of component (C) in monomeric and oligomeric form, as well as a mixture of mixed oligomeric allyl carbonates and allyl phthalates of component (C), the relative quantities of said constituents of the present composition mainly depending on the pre-selected ratios of the reagents (A), (B) and (C).
The above composition can be transformed into organic glass, by means of radicalic polymerization, using the normal xe2x80x9ccastingxe2x80x9d technique: said organic glass therefore represents a further object of the present invention.
For this purpose, one or more polymerization initiators, soluble in the composition and capable of generating free radicals within a temperature range of 30xc2x0 C. to 120xc2x0 C., are added to said composition.
A group of polymerization initiators useful for the purposes of the present invention is the peroxide group.
Preferred examples of peroxides which can be used for the purposes of the present invention are: dicyclohexylperoxydlcarbonate, diisopropylperoxydlcarbonate, dibenzoylperoxide, di(s-butyl-peroxydicarbonate, s-butyl-cyclohexylperoxydicarbonate, etc.
Other peroxides which can be used for the purposes of the present invention are perketals.
Preferred examples of perketals useful for the purposes of the present invention are: 1,1-di-(t-butylperoxy)cyclohexane, 1,1-di-(t-butylperoxy)-3,3,5-tri-methylcyclohexane, 1,1-di-(t-amylperoxy)cyclohexane, 1,1-di(t-butylperoxy)-2-methylcyclohexane, 1,1-di-(t-amylperoxy)-2-methylcyclohexane, etc.
The quantity of initiator used can generally vary within a range of 1 to 6 parts by weight for every 100 parts by weight of the composition object of the present invention.
The composition object of the present invention may optionally contain one or more conventional additives such as, for example, oxidation, light and heat stabilizers, lubricants, dyes, pigments, ultraviolet light absorbers (UV-absorbers), infra-red radiation absorbers (IR-absorbers), and the like, in a total quantity however of not more than 1 part by weight for every 100 parts by weight of the compositions themselves.
Examples of additives which can be used for the purposes of the present invention are: sterically hindered phenols, sterically hindered amines, benzophenones, benzotriazoles, organic phosphates and phosphonites, etc.
The composition object of the present invention containing the polymerization initiator and, optionally, one or more additives selected from those mentioned above, is transformed into the relative organic glass, operating at a temperature ranging from 30xc2x0 C. to 120xc2x0 C., with polymerization times which generally vary from 1 hour to 100 hours.
During the polymerization, limited volume contraction phenomena occur and the organic glass thus obtained has a refractive index (nD20)xe2x89xa71.53, good optical and physico-mechanical properties and good dyeability.
Said organic glass is particularly useful in the production of optical articles such as ophthalmic lenses and lenses for optical instruments: these end-products therefore form an additional object of the present invention.
The advantages deriving from the use of the polymerizable liquid composition object of the present invention with respect to the use of compositions of the known art are mainly the following:
first of all, the optical articles obtained have no internal tensions when tested in polarized light;
secondly, the lenses obtained, after immersion in color baths, have homogeneous shades and do not have any defects of a cosmetic nature.
Some illustrative examples are provided for a better understanding of the present invention and for its embodiment, but should not be considered as limiting the scope of the invention in any way.
In the following examples, polymerizable liquid compositions are prepared by reacting, under transesterification conditions, a mixture of diallyl carbonate (A) and a phthalic ester (B) with one or more aliphatic polyols (C).
The polyol (C) used in the examples is indicated each time, as also the possible addition of allyl alcohol.
A peroxide polymerization initiator whose nature and concentration are indicated each time in the following experimental examples, is added to the liquid compositions thus obtained.
The compositions containing the polymerization initiator are transformed, by means of polymerization, into flat plates having a thickness of 3 mm or neutral lenses, using the casting technique. Operating according to this technique, the liquid compositions, containing the polymerization initiator, are poured into the cavity of a mould consisting of two glass elements and having a spacer seal made of plasticized polyvinylchloride, ethylene-vinylacetate (EVA) copolymer, low density polyethylene (LDPE), or another suitable material, compatibly with the operating conditions.
The liquid compositions are then subjected to polymerization by means of thermal treatment in a forced circulation oven, as described hereunder in the experimental examples.
At the end of the above treatment, the moulds are opened and the polymerized products are recovered and maintained at 110xc2x0 C. for two hours to complete the polymerization reaction and give the end-product dimensional stability.
The following characteristics are determined on the plates thus obtained:
(a) Optical Characteristics
Refractive index (nD20): measured with an Abbe refractometer (ASTM D-542).
Yellow index (YI) (ASTM D-1925) defined as:   YI  =            100      Y        ⁢          (                        1.277          ⁢          X                -                  1.06          ⁢          Z                    )      
xe2x80x83determined with a Macbeth 1500 Plus spectrophotometer.
(b) Physical and Mechanical Characteristics
Density: determined with hydrostatic scales at a temperature of 20xc2x0 C. (ASTM D-792).
Shrinkage in polymerization calculated with the following formula:       %    ⁢          xe2x80x83        ⁢    shrinkage    =                    (                              polymer            ⁢                          xe2x80x83                        ⁢            density                    -                      monomer            ⁢                          xe2x80x83                        ⁢            density                          )                    (                  polymer          ⁢                      xe2x80x83                    ⁢          density                )              xc3x97    100  
Rockwell Hardness (M) measured with a Rockwell durometer (ASTM D-785).
Izod shock resistance without notch (ASTM D-256 modified)
(c) Thermal Characteristics
Deflection temperature under load 1.82 MPa (HDT) (ASTM D-648).
(d) Dyeability
The capacity of the material to absorb a dye on its surface is determined, by immersion (xe2x80x9cdip-dyeingxe2x80x9d) of a neutral lens in an aqueous bath in which the dye BPI Gray is dispersed.
For this purpose, the lens is immersed in said color bath for 10 minutes at a temperature of 80xc2x0 C. and, after rinsing with demineralized water, the homogeneity of the lens color is determined by sight observation.
From the examples described below, it can be clearly seen that the compositions object of the present invention, as well as having a reduced volume contraction in polymerization, allow the production of organic glass with improved characteristics with respect to the organic glass of the known art:
refractive index higher than that of the organic glass obtained from the polymerization of bis(allyl carbonate) of diethylene glycol;
low yellow index;
high impact strength;
good dyeability and color homogeneity.